Method of manufacturing cellulose according to the sulphite method



June 9, 1931. T. E WAENERLUND 1,809,499

METHOD OF MANUFACTURING CELLULOSE ACCORDING TO THE SULPHITE METHOD Filed Sept. 8, 1930 J. E.Wa er1er/un/ Patented June 9, 1931 UNITED STATES Basses) PATENT OFFICE TORSTEN E. WAENEBDUND, OF ORNSKOLDSVIK, SWEDEN, ASSIGNOB TO M O OCH DOMSJC AKTIEBOLAG, OF OBNSKOLDSVIK, SWEDEN METHOD OF MANUFACTURING CELLULOSE ACCORDING TO THE SULPEITE METHOD Application filed September 8, 1930, Serial No. 480,530, and in Sweden February 20, 1929.

The present invention refers to a method of cooking sulphite-cellulose which has for its object to utilize the heat of the waste gases and the waste lye from the digester or boiler for manufacturing a sulphite liquor (cooking acid) with a very high percentage of S0 The characteristic feature of the invention consists in this that the raw sulphite liquor or raw acid, which as known contains calcium bisulphite and free SO as-it comes from the acid towers and before being introduced into the boiler is caused to pass through an absorption tower where it is enriched with SO coming partly from the waste gases escaping from the boiler and partly from heated acid, whereafter the raw acid, after having been enriched with SO in this manner, is caused to pass through a pre-heater being heated by means of waste gases and waste lye from theboiler. The raw acid having been treated in such a manner is then'introduced into a storage receptacle from which the same, after having been further heated, if necessary, may be directly carried over to the boiler, or even it is first introduced into a second receptacle which is maintained filled with acid, the acid in said receptacle being held in continuous circulation through a pre-heater, so that it is heated to the required temperaturev suitably IOU-120 0., before being introduced into the boiler.

A form of embodiment of the method is described in the following specification, reference being had to the accompanying drawing, where an apparatus system for the execution of the method is schematically shown. This apparatus system also forms part of the invention.

Through the conduit 58 raw acid is supplied from the acid towers (not shown) to the receptacle 2 from which said acid is through the conduit 3 pumped over to the top of the absorption tower 4 which for effecting a good absorption is filled with acid-proof material, for instance so called spiral bodies. To the lower end of the absorption tower are connected two pumps 7 and 8, one 7 of which causes a quantity of acid controlled by the valve 20 to circulate'either'through the whole tower or through a certain part of the lower end of the same, which may be regulated by the valves 21 and 22. The other pump 8 has its suction tube situated on a higher level than the suction tube of the pump 7 and forces the acid through the pre-heater 5 and from there through the conduit 5a to the receptacle 72. The pre-heater 5 is provided with a heating element consisting of tubes. Through the same is forced through the conduits 50 and 51 as a heating medium partly lye taken out from the boiler during the cookin operation, partly gases escaping from the boiler during the cooking operation and partly hot waste lye which is taken out from the oiler after finished cooking. These gases and liquids give off one part of their heat to the cooking acid. In order to obtain a higher temperature difierence in the pre-heater between the heating medium and the cooking acid the currents of lye and gases are regulated by meansof the valve 23 in the conduit 52 between the pre-heater and the absorption tower 4, the valves 5354 located before the pre-heater being then fully opened. By this means the heat delivering medium will have the same temperature as the content of the boiler when it passes through the pre-heater.

From the pre-heater 5 cooled lye and waste gases are ledthrough the conduit 52 to the lower part of the absorption tower 4, whereafter in this tower the S0 gas is absorbed by the raw acid circulating through said tower. The upper part of the absorption tower is through the conduit 40 connected with the acid tower, so that SO gaseswhich may not have been absorbed in the absorption tower are recovered and utilized in the acid tower.

Those parts of the waste lye and of the condensate from the gases, which are not to be mixed with the raw acid are removed from the conduit 52 through the valve 24 and conduit 55. v

The acid which has been enriched with free SO, in the absorption tower 4 is pumped in the previously indicated manner through the pre-heater 5 to the receptacle 72 into which it enters pre-heated to a temperature of about 5060 C. In order to avoid the formation of a vacuum and of too high a pressure at varying liquid levels in the receptacle 72 the gas chamber of the latter is b by means of an automatically acting valve 28 and the-conduit 42 connected with the gas chamber a of the absorption tower, so that the acid receptacle 72 is through the absorption tower put into connection with the gas conduit 40 of the acid tower. Throu h the conduit 57 the waste gases from the" oiler may be introduced into the acid in the lower part of the receptacle 72.

From the receptacle 72 the acid may be carried over to the receptacle 73 which latter is continuously filled with cooking acid heated to about 100120 C. The carrying over of the acid from receptacle 72 to receptacle 7 3 is executed in connection with the filling of the boiler with acid. Then the valves 25, 26 and 27 are opened so that the acid is forced by means of the pump 9 from the receptacle 72 to the bottom of the receptacle. 73, where it forces out hot acid from the latter, which hot acid through the valve 27 and the conduit 41 is brought over from the top of the receptacle 73 and into the'boiler. The pumping continues until the boiler is filled with acid, whereafter the pump is stopped and the last mentioned valves are closed. The receptacle 73 is then still filled with acid which is colder in the lower part of the same than in the upper part.

The heating of the cooking acid in thereceptacle 73 takes place indirectly by means of steam from the conduit 56 in the preheater 6 through which acid is held in circulation through the conduit 43 and the pump 10. A dangerous pressure which may be created during the heating operation is.

balanced by means of any suitable arrangement, for instance a conduit 44 between the bottoms of both the receptacles and a valve 39 in said conduit. f

It is evident that several variations of the process are possible without departing from the scope of the invention. Thus for instance it will be possible to use instead of the absorption tower 4 several such towers of inferior height each such tower of low height working in the same manner as above described in connection with the absorption tower 4. Moreover, it is not necessary to use the receptacle 73 in which case only the receptacle 72 is used and is then connected with the pro-heater 6 in the same manner as shown in the drawing in connection with the receptacle 73 sothat the acid will be suifi ciently heated before being introduced into the boiler. However, from several points of view it may be advantageous to use two receptacles 72 and 73, as the counter pressures will be more favourable and, moreover, a purer acid may be taken out from the receptacle 73 if the latter cooperates with the receptacle 72 than would be the case if acid was taken out directly from the latter. If

- and lye, after having given 0 necessary the acid may be further heated etween the receptacles 72 and 73.

Besides the advantages in respect of heat economy and with regard to the possibility of obtaining an acid containin a high percentage (8% or more) of'free S 2 the invention offers the following advantages:

The removing of the gases from the boiler may take place in a more quick and complete manner due tothe fact that the counter pressure may be regulated as far as down to'the atmospheric pressure. --Previously the waste gases have as a rule after cooling been introduced directly into the acid receptacles in which case partly the absorption has been very bad and partly the removing of the gases from the boiler has been very slow due to an increasing counter pressure.

Due to the fact that the finished cooking acid is taken out from the top of the receptacle 73 the same may be freed from sludge and other impurities being injurious for the cooking operation. This is rendered possible in such a manner that the circulation pump 10 is stopped some minutes before the boiler is to be supplied with acid in order that sludge and other heavy impurities may sink to the bottom from which they may be removed from time to time.

I claim:

1. Method of manufacturing cellulose by COOklIlg cellulosic material with a cooking acid of high percentage of free sulphuric acid, comprising causing the cold raw acid, before introducing the same into the boiler, to pass through an absorption apparatus, enriching the same in said apparatus with S0 at atmospheric pressure passing the acid thus enriched through a heat transmission apparatus, introducing into said apparatus as heating medium warm waste products from the boiler and leading said heating medium, after it has given off heat to the acid, into the absorption apparatus, forcing the acid thus enriched and heated into a storage receptacle, heating the same and introducing it into the boiler for cooking cellulosic material therewith under pressure.

2. Method of manufacturing cellulose by cooking cellulosic material with a cooking acid of high percentage of free sulphuric acid, comprising causing the cold raw acid, before introducing the same into the boiler, to pass through an absorption apparatus, circulating said acid through said apparatus so as to enrich the same with S0 at atmospheric pressure, forcing the acid thus enriched through a heat transmission apparatus, leading through said apparatus as heating medium hot waste gases and waste lye from the boiler and introducin such gases f heat to the acid, into the absorption apparatus, forcing the acid thus enriched and heated into the lower part of a storage receptacle, forcing such acid therefrom into the lower part of another storage receptacle, circulating the acid in said receptacle through a heating element, leading off acid from the top portion of said receptacle and into the boiler and cooking cellulosic material therewith in said boiler.

' 3. Apparatus system for making sulphite 1i uor '(acid). with high percentage of free S3 comprising in combination an absorption apparatus, a heat transmitting apparatus and a storage tank, means for introducing raw acid from the acid tower into said absorption apparatus, means for circulating the acid within said apparatus, means for leading through said heat transmitting apparatus waste gases and lye from the boiler and means for introducing the same into the absorption apparatus, means for forcing the enriched and heated acid from the absorption apparatus through the heat exchange apparatus and therefrom to a storage tank and means for further heating the acid and for forcing it into the boiler.

4. In an apparatus system according to claim 3 the combination with the receptacle receiving heated and enriched acid from the heat changing apparatus of a second receptacle for acid, means for carrying over acid from said first receptacle to the second receptacle, means for circulating the acid in the second receptacle through a heating element and means for forcing the acid from the top of the second receptacle into the boiler.

In testimony whereof I have hereunto affixed my signature.

TORSTEN E. WAENERLUND. 

